It might be very helpful for plugin developers, because in my own code I have a lot of warnings when I use this plugin.

The error is really common, so the need is quite high.
Since it does not have any 3rd party dependencies, we are also free to just move it to mypy/plugins

We can also add a note about it in the docs: https://mypy.readthedocs.io/en/stable/extending_mypy.html